The present invention relates to industrial circuit breakers and particularly to apparatus enabling the breaker operating mechanism to sustain a charge against a de-energized undervoltage release solenoid.
In addition to protecting load circuits from a wide range of overcurrent conditions, circuit breakers are often called upon to protect voltage sensitive loads, such as motors, from sustained undervoltage conditions. To this end, circuit breakers are equipped with undervoltage releases (UVR) operating to trip the breaker in response to an abnormally low voltage condition. Such UVRs traditionally take the form of a solenoid whose coil is energized from the line voltage. Its plunger is biased to an extended position by the calibrated force of a spring. With the plunger in its retracted, seated position, as long as the line voltage remains substantially at its nominal level, the electromagnetic force developed by the solenoid overpowers the spring to maintain its plunger seated in its retracted position. When the line voltage drops to a sustained abnormally low level, the spring then becomes overpowering, and the plunger is pulled to its extended position. A trip member, linked to the plunger, is incidentally shifted to a trip position precipitating conditioning of the breaker latch to discharge or trip the movable contact operating mechanism, and the movable contacts are abruptly propelled to their open position.
Before the operating mechanism can be recharged, the solenoid plunger is forcibly returned to its seated position, in the process shifting the trip member out of its trip position, so as to allow the latch to reset to a condition enabling it to sustain a charge imparted to the operating mechanism. However, if the line voltage remains abnormally low, the spring immediately pulls the UVR plunger to its extended position, shifting the trip lever to its trip position. The latch is thus defeated, and the charge imparted to the operating mechanism is dumped, causing the mechanism to crash. If the circuit breaker is equipped with a motor operator mechanism to effect recharging of the breaker operating mechanism and it is programmed to automatically execute a charging cycle each time the breaker is tripped open, the operating mechanism is repeatedly charged and crashed under a sustained undervoltage condition, leading ultimately to failure of the equipment. While it would be advantageous to permit the operating mechanism to sustain a charge in the face of a sustained undervoltage condition, it is deemed important that the breaker not be permitted to close back in on such a sustained undervoltage condition.
It is accordingly an object of the present invention to provide apparatus for locking out an undervoltage release such as to permit a circuit breaker operating mechanism to sustain a charge despite a prevailing undervoltage condition.
A further object is to provide undervoltage release lockout apparatus of the above character which nevertheless prevents breaker closure into a prevailing undervoltage condition.
An additional object is to provide UVR lockout apparatus of the above character which includes improved means for reliably resetting the undervoltage release automatically as the circuit breaker is tripping open.
Another object is to provide UVR lockout and reset apparatus of the above character which is efficient in construction and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.